Active Noise Reduction (ANR) is sometimes called Active Noise Cancellation. By determining the characteristics of sources of linear acoustic energy, and the sound field which exists in a region of space which has a linear relationship to the source acoustic field, the complex temporo-spatial acoustic field at the measurement point (such as the position of a person's ear) may be modified with an acoustic field which is 180 degrees out of phase from the source field. Thus the total amplitude of the sound field experienced at the ear point is reduced.